Observational study finds multivitamin use not associated with a lower mortality rate

"Multivitamin Use and Mortality Risk in 3 Prospective US Cohorts" led by researchers at the National Institutes of Health's National Cancer Institute, was published recently in JAMA Network Open. The study tracked about 390,000 healthy U.S. adults via questionnaires for 20 years.

Details 

The population studied included adults pooled from three prospective studies: The National Institutes of Health–AARP Diet and Health Study (NIH-AARP) cohort; the PLCO Cancer Screening Trial cohort; and the Agricultural Health Study (AHS) cohort. The participants were generally healthy and anyone who had a chronic condition when they enrolled was excluded from the analysis.

Variations across observational studies may exist due to differences in multivitamin composition or confounding. The researchers said the study addressed these concerns by harmonizing and pooling complete data from participants in large cohorts, evaluating potential differences in relative risk by demographic and lifestyle factors, and evaluating the long-term association of daily multivitamin use with mortality risk.

Findings 

The analysis showed that people who took daily multivitamins did not have a lower risk of death from any cause than people who took no multivitamins. There were also no differences in mortality from cancer, heart disease, or cerebrovascular diseases. The results were adjusted for factors such as race and ethnicity, education, and diet quality.

The researchers noted that it is important to evaluate multivitamin use and risk of death among different kinds of populations, such as those with documented nutritional deficiencies, as well as the potential impact of regular multivitamin use on other health conditions associated with aging.

Of the 390,124 people involved in the three studies, half of them were 61 years or older when the studies began. 

Those who took multivitamins differed from non-users in various ways. Multivitamin users were more likely to be women, college-educated, non-smokers, exercise regularly, have a healthier diet, lower body mass index and take individual vitamin and mineral supplements. 

After adjusting for these differences, it was found that non-users had the lowest risk of death. Daily multivitamin users had a 4% higher mortality rate, while those who took them less frequently had a 9% higher rate. Younger vitamin users, under the age of 55, had a 15% higher mortality rate. However, no statistically significant differences were observed in mortality risks between the three groups over a longer period of 15 years.

Limitations

The researchers acknowledged some limitations, noting that the study was observational and based on questionnaires. This may have residual confounding and bias risk estimates due to poorly measured or unmeasured confounders. However, the researchers pointed out that they excluded individuals with a history of cancer and other chronic diseases and adjusted for major mortality risk factors in our analyses. There is also a possibility of exposure misclassification due to faulty memory of sporadic multivitamin usage. Additionally, selection bias is possible as the participants with missing data could be systematically different than those with complete data. Another limitation is the studies mostly included White participants, but the researchers said  pooling across studies improved statistical power. Lastly, the researchers acknowledge that they cannot assess latency of the association of multivitamin use and the cumulative association over the life span. 

Other research points to benefits 

Commenting on the new study, Steve Mister, president and CEO of the Council for Responsible Nutrition (CRN), said: "Multivitamins are a vital component of Americans' health regimens. The evidence supporting their benefits is robust, compelling, and continues to grow."

Indeed, previous large-scale randomized trials on multivitamin use have shown multivitamin use to be beneficial in a variety of ways. For instance, one study published in the Journal of Nutrition​​ found long term daily multivitamin use was associated with a 44% lower risk of major cardiovascular events such as heart attack and stroke.

Other research, such as the Physicians’ Health Study (PHS) II study, published in JAMA​​, found that multivitamin supplements may reduce the risk of cancer by 8%.

The COSMOS study, published recently in the American Journal of Clinical Nutrition​​, found that daily multivitamin supplementation may boost episodic memory and slow cognitive decline in older adults. 

Beyond mortality rates 

Andrea Wong, Ph.D., SVP, Science and Regulatory Affairs, CRN, told NutraIngredients-USA that the focus should be placed on the substantial evidence that looks beyond mortality rates. 

“Extensive evidence shows multivitamins play a crucial role in meeting nutritional needs, lowering the risk of various diseases and health issues, and enhancing overall well-being,” said Wong. “Focusing solely on mortality rates overlooks the numerous health benefits demonstrated in rigorous scientific research, such as reducing birth defects, decreasing cancer risk, and mitigating cognitive decline. Multivitamins are an essential part of health routines for Americans with strong and increasingly persuasive evidence supporting their benefits.”